Laboratory-scale continuous reactor for soluble selenium removal using selenate-reducing bacterium, Bacillus sp. SF-1

Area of Science:

• Environmental Microbiology
• Bioremediation Technology
• Biochemical Engineering

Background:

• High concentrations of soluble selenium (selenate/selenite) pose significant environmental toxicity.
• Effective bioremediation strategies are needed to remove toxic selenium species from wastewater.
• Bacillus sp. SF-1 is identified as a promising selenate-reducing bacterium.

Purpose of the Study:

• To construct and evaluate a continuous flow bioreactor for removing high concentrations of toxic soluble selenium.
• To investigate the effect of cell retention time on selenium reduction efficiency by Bacillus sp. SF-1.
• To develop a mathematical model for assessing selenium reduction kinetics.

Main Methods:

• Construction of a 0.5 L continuous flow bioreactor operated as an anoxic, completely mixed chemostat.
• Cultivation of Bacillus sp. SF-1 with selenate as the electron acceptor and lactate as the carbon source.
• Operation of the bioreactor at varying cell retention times (2.2–95.2 h) to assess selenium removal.

Main Results:

• Selenate removal was observed at short cell retention times, but selenite accumulated.
• Complete reduction of both selenate and selenite to non-toxic elemental selenium was achieved at long cell retention times.
• First-order kinetic constants for selenate and selenite reduction were determined, along with bacterial cell yield.

Conclusions:

• Continuous flow bioreactors utilizing Bacillus sp. SF-1 are effective for high-concentration soluble selenium removal.
• Optimizing cell retention time is critical for preventing intermediate accumulation and ensuring complete selenium reduction.
• The developed mathematical model provides insights into the bioreduction kinetics of selenium species.